Verga, that was the dialogue (between God and Satan) Pope Leo XIII claimed he heard as he descended the altar that inspired him to compose the Prayer to Saint Michael. The old "Leonine Prayers" at the end of mass were the result of this "vision." They were chucked, along with much else, as a result of the Second Vatican Council.
Thank you for clarifying. My only excuse is that I was not familiar with that particular reference and that it has been a very long week at work. My apologies.